Synthesis of Hard-Magnetic Material of the Fe–Cr–Co System Made of a Spherical Powder

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Abstract—A short-cut method of synthesis of a hard-magnetic material made of a spherical powder of the 25Cr–15Co–Al–Nb alloy obtained by spraying a melt with a stream of gas was proposed. It was established experimentally that uniaxial pressing of the powder in the initial state did not allow obtaining compacts without defects despite of the split die and pressing pressure up to 600 MPa. Application of powder annealing in hydrogen at 800°C decreases the hardness of the material particles. However, when compacting, the similar separation of compacts is observed as with the original powder. The use of a plasticizer gives a positive effect for improved compactibility, but it reduces the values of magnetic hysteresis characteristics. It is shown that the mechanical activation of spherical powder in a planetary mill allows obtaining the high-quality compacts and sintered specimens with high values of magnetic characteristics. The changes in the morphology of the powder particles during processing are revealed. Enlargement of powders due to cold welding is observed; the shape of particles changes dramatically as compared to the original powder. The particles size spread is substantially smaller in comparison with the original spheres; a heteraxial character is observed. Application of balls of larger diameter for grinding leads to better results. The magnetic hysteresis characteristics of hard-magnetic material synthesized from an alloy powder mechanically activated for 80 min are at a high level which ensures its technical application: residual induction B_r = 1.18 T; coercive force Н_сВ = 43.1 kA/m; maximum magnetic product (ВН)_max = 31.8 kJ/m³.